Infrared Excitation of Visible Luminescence inY1−xErxF3via Resonant Energy Transfer

Abstract

The temperature and concentration dependences of the visible emission of ${\mathrm{Er}}^{3+}$ in Y${\mathrm{F}}_3$ under infrared excitation of the ${}_{}{}^4{}_{}{}^{}I_{\frac{11}{2}}^{}{}_{}{}^{}$ levels have been measured. The infrared radiation is absorbed by ions initially in the ground state and two excitations subsequently combine, yielding an ion in a higher-energy state. The temperature dependence of the ${}_{}{}^4{}_{}{}^{}S_{\frac{3}{2}}^{}{}_{}{}^{}\to {}_{}{}^4{}_{}{}^{}I_{\frac{15}{2}}^{}{}_{}{}^{}$ emission has a broad maximum at 90°K. The reduction in the emission for $T<\mathrm{}90\mathrm{}$°K results from the depopulation of the higher-energy crystal-field-split levels of the ${}_{}{}^4{}_{}{}^{}I_{\frac{11}{2}}^{}{}_{}{}^{}$ manifold which have a resonant match with the ${}_{}{}^4{}_{}{}^{}F_{\frac{7}{2}}^{}{}_{}{}^{}$ levels. For $T>\mathrm{}90\mathrm{}$°K the emission is increasingly quenched by ion-pair relaxation from ${}_{}{}^4{}_{}{}^{}S_{\frac{3}{2}}^{}{}_{}{}^{}$ via ${}_{}{}^2{}_{}{}^{}H_{\frac{11}{2}}^{}{}_{}{}^{}$. For the concentration range $0.01<x<\mathrm{}0.1\mathrm{}$, the ${}_{}{}^4{}_{}{}^{}S_{\frac{3}{2}}^{}{}_{}{}^{}$ emission is proportional to $x^{2.9}$ at 77°K and to $x^{1.3}$ at 295°K.